Garnet compositions



3,419,496 atented Dec. 31, 1968 GARNET COMPOSITIONS Avnir Vassiliev, Jean Nicolas, and Mieczyslaw Hildebrandt, Paris, France, assignors to CSF-Compagnie Generale de Telegraphie. Sans Fil, a corporation of France No Drawing. Filed Mar. 31, 1965, Ser. No. 444,437 Claims priority, application France, Apr. 22, 1964,

4 Claims. (Cl. 252-6257) ABSTRACT OF THE DISCLOSURE Garnet compositions having a resistivity higher than in known materials of this kind thus reducing considerably the dielectric losses. In these compositions are introduced paramagnetic ions Fe and Mn, in molecular proportions defined by the general formula where in mole proportion. These garnet compositions are used in non-reciprocal devices such as i solators, phase shifters, or circulators for ultra-high frequency electromagnetic waves.

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The present invention relates to garnet compositions. More particularly it relates to garnet compositions for use in non-reciprocal devices such as isolators, phase shifters or circulators for ultra-high frequency waves.

It is an object of the invention to provide a garnet composition providing a resistivity higher than in known materials of this kind, thus considerably reducing dielectric loss which usually limits the performance of such devices.

It is another object of the invention to provide a method for preparing such compositions.

With the other performances remaining comparable the invention provides a resistivity gain by a factor which may easily exceed 1000.

This is most important, in particular for the design of circulators such as the so-called Y type circulators (because they are provided with three channels) intended, in particular, for multiplex radars, especially when combined with masers.

It is known to use in this kind of application yttrium garnets and garnets containing some other trivalent ions, such as 6d and sometimes Al+++. In the case of these garnets great care was taken to avoid introducing, for example, any foreign paramagnetic ion, for fear of prohibitively widening the resonance line, the latter being relatively narrow when these materials are pure and properly prepared.

According to the invention, on the contrary, there are introduced in garnets of this type paramagnetic ions Fe and Mn, in molecular proportions defined by the general formula:

where 0.3 x 0.6 0.0Q5 e 0.020 0.1 y 1 in mole proportion.

The invention alter concegns a method of preparation of such garnets which is remarkable in that it includes thermal treatment in an oxygen atmosphere at a temperature between 1365 and 1385 C.

. The invention will be better understood by means of the following description.

The raw materials used have to have a high degree of purity preferably higher than 99%. Oxides Y O and Gd O in particular have to be free of any impurity of the type Eu O H0 0 Dy O This precaution is necessary to ensure narrow resonance lines. 7

The raw materials, taken in proportion defined by the above formula, are crushed in steel jars containing steel balls, in the presence of distilled water, for 24 hours.

The resulting mixture is dried out and is then presintered over 1000 C. for two hours, preferably at 1200 C.

After crushing as above, but for 48 hours, followed by drying and mixing with a 15% polyvinyl alcohol solution in water (10% solution), the product is converted to a fine granulate. The latter is pressed in steel moulds to the desired shape and is sintered in oxygen atmosphere at 1380 C. for 2 hours, followed by cooling down at the rate of 50 C. to C. per hour.

The following table shows a number of examples of compositions, in which:

x=0.5 and 5:0.015

The resistivity p of the resulting garnets, expressed in megohm-centimetres was measured on discs about 20 mm. in diameter and 2 mm. thick. The two sides of the discs were ground and silvered and the measurement effected by means of a megohm-meter.

The width of the resonance line AH was measured at about 9500 mc./s. in a resonant cavity on samples in the form of spheres 1.5 mm. in diameter, placed 'at a node of an ultra-high frequency magnetic field.

y in mole percentage pMt'Zcm. A 11.0.,

It will be noted that for values of y greater than 1 p decreases. while AH is hardly altered, this being a surprising and quite remarkable result.

It is to be understood that the details of the method of preparation may be varied without departing from the spirit and scope of the invention.

What is claimed is: 1. A garnet composition defined by the general for- 'mula:

3 [1x)Y O; X Gd203] I-G) Fe O yMnO where:

x is between 0.3 and 0.6 e is between 0.005 and 0.020 y is between 0.1 and 1 in mole proportion 3. A method for preparing garnets comprising the following steps: presintering at above 1000 C. for about 2 hours a mixture of compounds defined by the formula:

al i

where x is between 0.3 and 0.6, e is between 0.005 and 0.002 and y is between 0.1 and l in mole proportion to obtain a pre-sintered mixture; crushing said pre-sintered mixture and shaping it by pressing to obtain a pressed mixture; sintering said pressed mixture in oxygen atmosphere at temperatures between 1365 and 1385 C. for about 2 hours; and cooling said pressed mixture at a rate of 50 to 150 C. per hour.

4. A method for preparing a garnet composition for use with ultra-high frequency waves comprising the steps of pre-sintering at about 1200 C. for about 2 hours a mixture of compound defined by the formula:

where x is between 0.3 and 0.6, e is between 0.005 and 0.20 and y is between 0.1 and 1 in mole proportion to ob- 4 tain a pre-sintered mixture, crushing said pre-sintered' mixture and shaping it by pressing to obtain a pressed mixture, sintering said pressed mixture in oxygen atmosphere at temperatures between 1365 and 1385 C. for about 2 hours and cooling said pressed mixture at a rate of 50 to 150 C. per hour.

References Cited UNITED STATES PATENTS 3,007,874 11/1961' Peyssou et 'al 25262.56 3,038,861 12/1962 Van Uitert 25262.57 3,232,877 2/1966 Vassiliev et a1 25262.56

TOBIAS E. LEVOW, Primary Examiner.

R. D. EDMONDS, Assistant Examiner. 

